Gradle for Java-Based applications and libraries

Project structure for gradle project in Java

• single Java project with Gradle

  • example:

    root
     + src
       + main
       + java
       + resources
  
       + test
         + java
       + resources
     + build
       + classes    -> compiled class files
       + libs       -> generated JAR files

• A multi-modules project file structure:

  • example:

    root/
     + appA/
        + build.gradle
           + src/
           + main/
           + java/
           + resources/
           + test/
           + java/
           + resources/
        + build/
           + classes/    -> compiled class files
           + libs/       -> generated JAR files
     + appB/
        + build.gradle
        + src/
       ... (same as above subproject)

In build.gradle

JAVA plugin

• add plugins:

    plugins {
      id 'java'
    }

• set the Java compatibility:

    java {
      sourceCompatibility = JavaVersion.VERSION_11
      targetCompatibility = JavaVersion.VERSION_11
    }

• compiler arguments:

    compileJava {
      // example: to terminate compilation if a warning occures)
      options.compilerArgs << '-Werror'
    }

• set JAR filename explicitly:

    version = '1.0.0'
  
    jar {
      archiveBaseName = '<your-project-name>'
    }

Set javadoc options:

javadoc {
  options.header = '<your java doc title here>'
  options.verbose()
}

APPLICATION plugin

• in build.gradle file:

    plugins {
      id 'application'
    }

• set base class to run for the application as needed by plugin:

    application {
      mainClass = 'com.<organization>.<project>.Main'
    }

• in settings.gradle file:

    rootProject.name = '<project_name>'
    include ':appA', ':appB'

Commands

• gradle wrapper -> Create Gradle Wrapper

• gradle clean -> Clean dist output?

• with java plugin:

  • ./gradlew compileJava --console=verbose
  • ./gradlew processResources --console=verbose

• or both above command agragated command:

  • ./gradlew classes --console=verbose

• see dependencies tree (and if it can be found)

  • ./gradlew dependencies

• generate JAR file

  • ./gradlew jar -> dropped JAR in build/libs directory

• with application plugin:

  • ./gradlew run --args="add 1 2" -> specifies arguments
  • ./gradlew installDist -> generate shippable application with scripts
  • ./gradlew distZip distTar -> bundle distributhe appliation
  • ./gradlew javadocs -> genetate java doc in build/docs/javadoc (index.html)

• project or multi-modules project:

  • ./gradlew project -> show project and show projects structure

Maven Dependencies

• where to find? [https://search.maven.org]

• dependency coordinates:

  • example: commons-cli:commons-cli:1.4 -> <group>:<artifact>:<version> or GAV

• set the repositories (where to get from) and dependencies:

    repositories {
      mavenCentral()
    }
  
    dependencies {
      implementation 'commons-cli:commons-cli:1.4'  // get from maven repo search results
      implementation project(':appA')               // add project dependencies (other modules from this project)
      }

Testing with Gradle

JUnit 5 dependencies

• from search.maven.org:

• search org.junit.jupiter (latest version is 5)

  • minimum needed is junit-jupiter-api and junit-jupiter-engine

• declaring test dependencies:

  • testImplementation -> work on compilation and test execution
  • testRuntime -> work on runtime only

• adding dependencies:

  • copy & paste Gradle Groovy DSL path for both depenencies

    dependencies {
      implementation 'commons-cli:commons-cli:1.4' // not a testImplementation!
      testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'  // test dependency
      testRuntime 'org.junit.jupiter:junit-jupiter-engine:5.7.0'  // test dependency on run time only
    }

• commands:

  • ./gradlew compileTestJava -> compile tests
  • ./gradlew test -> run the tests (see useJUnitPlatform comment in order to use JUnit 5)
  • go to build/reports/tests/test the automaticaly gradle generated HTML report (index.html)
  • go to build/test-reults/test for the autmaticaly gradle generated XML test report

• adding test task in build.gradle:

    test {
      useJUnitPlatform()  // Java plugin expect Java 4 by default. Add useJUnitPlatform to indicates to use JUnit5 instead
  
      testLogging {
        events 'started', 'skipped', 'failed'  // will display specified events on run time
        exceptionFormat 'full'  // show stack trace on failures
      }
    }